This invention relates to the handling and control of a continuous web of photographic paper as it is moved through the processing steps required to develop exposed portions of the photographic paper to produce photographic prints. More particularly, the invention relates to an apparatus for controlling the amount of time that the paper spends in various baths associated with the developing process, regardless of the speed at which paper is fed to the developing baths from a photographic printer that runs at its own nonconstant rate.
In the photoprocessing industry photographic prints are produced on a continuous web of photosensitive paper that is exposed to the image-forming light in a printer. In most commerical photoprocessing laboratories the exposed paper is collected on a reel in a lighttight canister and carried from the printer to the developing baths that fix the image on the paper. It would be desirable to be able to run the paper from the photoprinter directly into the chemical baths without removal and manual handling of the film in order to speed the efficiency of the developing process by eliminating as many operator interventions as possible. One of the inherent problems in such a direct feed from the printer to the developing baths is the output of the paper from the printer is not usually a constant rate. The rate of output from the printer is affected by the type of operation occurring in the printer for any given batch of photos. At times the printer may be printing double prints of orders, while at other times the printer may be skipping over frames in the negative and printing only selected frames for reprints. The printer may be printing single prints from each frame. All of these different operations take different times to accomplish so that the speed of the printer is a variable with no advance predictability.
On the other hand, the developing process has very strict time constraints on it. For example, it is necessary to immerse the photographic paper in the various developing and fixing baths for precise amounts of time. In currently used developing systems the path through the baths is a fixed length. Therefore, the speed of travel of the web through the developing bath is a constant so that the paper travels the fixed length in a constant time. If the output of the printer were to be fed directly into the developing baths, a discrepancy would exist between the variable output rates of the printer and the necessity of constant rate within the developing bath. For this reason, current thinking on the subject proposes the use of large storage bins or buffers that would accept the output from the printer and build up a large enough stock of such exposed photographic paper that the paper could then be fed into the developing baths at a constant rate, while continuing to accept paper from the printer at an uneven rate, with the intermediate storage bin buffering the effect of the uneven printer output rate. One problem with this concept is that the large volume of photographic paper being processed each day in the lab requires a very large buffer or storage space, which is prohibitive due to the space constraints present in most laboratories or because of the inefficiency of having to lease additional space in order to handle the storage buffer. Also, it is undesirable to have large quantities of exposed but unprocessed paper contained in a relatively complex large buffer device that is subject to breakdowns.